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Logic Schematic "Four Counter" version of the EC-132 Calculator
June, 1965
This is a logic-level schematic for the Four-Counter version of the Friden EC-132 electronic calculator. The Four-Counter version of the EC-132 was an early implementation, with calculators after serial #3901 switching to the Three Counter architecture, eliminating the B counter and its control logic to simplify the machine.
The schematic includes all of the logic for the calculator at the gate and flip-flop level. The schematic includes only the logic circuitry located on the plug-in circuit boards, and does not include the power supply, details of the write driver and read amplifier for the delay line, as well as details of aspects of the CRT drive and deflection circuitry.
Given that the EC-132's logic is implemented entirely with discrete components the schematic uses unusual symbology and nomenclature to designate the logic elements. The general logic function is the OR gate, which is shown in the schematic as a box with an "O" at the top center. Boxes with an "I" in the top center are inverters. Boxes with "EF" are transistor emitter follower circuits, used on the output of gates to allow higher fanout capacity for gates that need to drive many other gate inputs. Boxes that are divided in half by a horizontal line represent flip flops. Other small boxes with diamond-shaped symbols on inputs are called AC gates, which operate on logic level transitions rather high or low states. The logic design is well described in the EC-132 Temporary Service Manual, as well as in the EC-130 Service Manual.
This schematic can be used in conjunction with the Four Counter Friden 132 Master Design Document (MDD, a.k.a. Computer Printout) to determine the actual components used for each logic gate and flip flop.
Any re-distribution of this document, printed or electronic, must include the watermark indicating its source as the Old Calculator Museum. Thank you.